NK Cells Lyse T Regulatory Cells in Human Infection with An Intracellular Pathogen (B167)

Abstract Previously we found that regulatory T cells (CD4+CD25+Foxp3+ cells, Tregs) expand in response to M.tuberculosis (M. TB) through mechanism that depend on prostaglandin E2 production. In the current study, we determined the role of NK cells in regulating Tregs expansion in human M. TB infection. M. TB whole cell lysate (TB lysate) resulted in regulatory T cell expansion (15.33±1.02% vs 1.5±0.22%, P<0.001). Addition of monokine-activated NK cells (IL-12, IL-15 and IL-18) markedly inhibited Treg expansion (6.2±1.2% vs 15±1.5%, P<0.001) but freshly isolated NK cells had no effect. NK cells activated with TB lysate-stimulated monocytes also reduced Tregs expansion (13.2±0.3% to 3.4±1.4%, P<0.001) confirming the physiological relevance of this effect. Reduced Tregs expansion was not due to inhibition of PGE2 production or because of IFN γ. Monokine activated NK cells lysed TB lysate-expanded Tregs, but not freashly isolated Tregs (% specific lysis of 21±3% vs 1±1% P<0.001), nor T regs depleted T cells. Anti-NKG2D and anti-NKp46 reduced the % specific lysis of expanded Tregs from 22±3% to 7±3% and 8±3%, respectively (P<0.001) but abs to CD16, DNAM-1, and 2B4 had no effect. NKG2D ligand, ULBP1 expression was markedly upregulated on expanded T regs, compared to T regs depleted cells ( 31±5% vs 2.1 ±0.4%, P=0.002) and freshly isolated Tregs (4.6±1.1%). Anti -ULBP1 significantly inhibited the NK mediated lysis of expanded Tregs (specific lysis of 27±4% vs 9±2%, P<0.001) but abs to ULBP2, ULBP3 and MICA/B had no effect. These finding suggest that NK cells reduce the frequency of M.TB-expanded T regs by direct lysis.